1. Statement of the Technical Field
The inventive arrangements relate to MOSFET circuits, and more particularly to a circuit for battery reversal operation and protection.
2. Description of the Related Art
Batteries are used as power sources in a wide variety of devices. Typically, these batteries are designed for user replacement. Although batteries are generally not difficult to replace, there is at least one potential installation error that can cause serious damage to equipment. Specifically, installation of a battery with the polarity reversed. This situation occurs when the positive terminal of the battery is connected to the negative power terminal of the equipment, and the negative terminal is connected to the positive power terminal of the device. Such an occurrence can prevent a system from operating and may cause damage to the equipment.
Various circuits have been proposed that provide operating and protection for circuitry from battery polarity reversal. For example, U.S. Pat. No. 4,139,880 to Ulmer et al. al., U.S. Pat. No. 4,423,456 to Zaidenweber, and U.S. Pat. No. 5,623,550 to Killion, each disclose a battery reversal operation and protection circuit. In general, each of these circuits is designed to provide a battery operated piece of equipment with proper power polarity, regardless of the way in which the battery is connected to the battery terminals of the equipment. In general, the circuits disclosed in the foregoing references are bridge rectifier type devices. However, rather than simply utilizing diodes, the circuits use either CMOS or MOSFET components to perform the rectification function.
One reason for utilizing CMOS or MOSFET type components for rectification is simply convenience. Where a device generally utilizes CMOS or MOSFET devices, it can be more convenient to use similar CMOS or MOSFET type components in the battery polarity reversal protection circuit. However, MOSFET devices in these applications can have other advantages as well. For example, the semiconductors used in bipolar devices can result in a significant variable voltage drop across the battery reversal circuit. This can be a problem for low power systems where low voltage drop and low power loss is desirable.
Despite the advantages offered by such MOSFET circuits that allow devices to operate with battery polarity reversed, they still suffer from certain drawbacks. For example, all of the referenced circuits have a rather limited input voltage operating range. This is due to the fact that for most MOSFET devices, the maximum voltage that can be applied between the gate and the source is rather limited. Gate to source voltages that exceed a specified value Vgs—max can damage the MOSFET components. This can be a problem with existing designs because practically the full value of the battery voltage will be applied across the gate to source terminals of the MOSFET. For example, in U.S. Pat. No. 4,139,880 to Ulmer et al. al., U.S. Pat. No. 4,423,456 to Zaidenweber, and U.S. Pat. No. 5,623,550 to Killion, the full value of the input voltage will be present between the gate and source terminals.